Production of potassium manganates



June 14, 1960 A. REIDIES ETAL PRODUCTION OF POTASSIUM MANGANATES Filed Oct. 10, 1956 Mnog C) H 0 VAPOGL I K MNO -KDH Sol'n I l I L 5 1 4 T K2MN4 Slurry HEAT g 4 Sol'n K2MNO4 Produci' INVENTORS: ARNO H. REIDIES MILTON B. CARUS limited States Patent 2,949,823 PRODUCTION OF POTASSIUM MANGANATES Arno H. Reidies and Milton B. Cams, La Salle, 111., as-

signors to Cams Chemical Company, La Salle, 111., a corporation of Illinois Filed Oct. 10, 1956, Ser- No. 615,033

14 Claims. (Cl. 23-58) The invention relates to the production of potassium manganates by oxidation of manganese compounds in an aqueous potassium hydroxide melt. More particularly, the invention relates to the production of potassium manganate (V) K MnO and to the production of potassium manganate (VI) K MnO by oxidation commencing with an oxidic manganese compound. The invention provides a process which renders production in such manner commercially practicable.

Prior to the invention, potassium manganate K MnO has been produced for many years, and several methods of production have been devised. A large part of the potassium manganate produced is subsequently converted to potassium permanganate. Fundamentally, the reactions involved in the prior production of potassium manganate and potassium permanganate are represented by the following equations:

The present invention is concerned with the production of K MnO according to ditierent equations, which also involve the production of K MnO The latter compound may be recovered for use as such or for production of K MnO therefrom.

Of the several methods proposed for manufacturing K MnO the primary commercial method apparently is the roasting method. This involves mixing hot concentrated potassium hydroxide and manganese dioxide, cooling and grinding the mixture. The concentrated potassium hydroxide starting material is produced by evaporating Water from aqueous potassium hydroxide up to 385 C. Alternatively, a slurry of 50% KOH and manganese dioxide is sprayed into a hot oven, and the product is cooled and ground. The ground product is then roasted at about 225 C. with air, while intermittently spraying water on the mixture. The roasting is carried out in large rotary drums or tubes. This operation requires a very large amount of equipment, with accompanying high capital investment, power, heat, labor and maintenance requirements. Furthermore, the process is slow, inconsistent and difiicult to supervise. The reaction cannot be carried to completion. This is apparently because of the difiiculty in supplying sufiicient water to the reactants and because sufficient potassium hydroxide cannot be supplied. As regards the former condition, the presence of water is-necessary for the reaction although it does not appear on the left of the equation. The potassium hydroxide quantity is limited, because over a certain ratio to manganese dioxide, the product agglomerates seriously and prevents further oxidation.

A number of years ago, a process was devised wherein manganese dioxide was oxidized to K MnO with air in a concentrated aqueous potassium hydroxide melt. Despite the potential attractiveness of such a process, it has apparently never been successfully employed on a com- 2,940,823 Patented June 14, 1960 mercial scale. This is very likely due to the fact that during the process, the mixture gets very thick or viscous,

, all. This thickening occurs within a period of several hours, even with a much reduced quantity of manganese dioxide in the melt.

We have now provided a process which overcomes the foregoing difiiculty of the prior melt oxidation process, and in doing so, have discovered the reasons for the difi'iculty and have provided a solution to the problems.

We have found that, apparently, the principal source of trouble is that the manganese dioxide swells up to many times its original volume after a short period of time. Even a small excess of manganese dioxide will swell up to convert the already somewhat viscous liquid into a thick paste.

We have discovered that the key to the solution of the problem is to add a manganese oxide to an aqueous potassium hydroxide melt at a rate of addition which is not substantially greater than its rate of oxidation to a valence above 4. In the new process, an oxidic manganese compound having a manganese valence of less than 5 is oxidized to K MnO wherein manganese has a valence of 5, the oxidic manganese compound being added at a rate not substantially greater than its rate of oxidation to K MnO We have further discovered that oxidation of an oxidic manganese compound having a manganese valence of less than 5, to K MnO is very desirably effected by reaction with a potassium manganate having a manganese valence of greater than 5, i.e., potassium manganate (VI) or potassium permanganate. The latter decomposes to potassium manganate (VI) very quickly under the reaction conditions, according to the equation 2KMI104 2K2MI104+ 2 2 In this manner, the oxidation of the manganese oxide is not dependent upon oxidation with a gas, such as air, and a favorable relatively low temperature may be employed for optimum results.

' The K MnO produced is further oxidized to K MnO The further oxidation may take place in the same reaction zone or vessel, concomitantly with or subsequent to the oxidation of the manganese compound having a valence below 5. Preferably, the oxidation of K MnO to K MnO is carried out in a separate reaction zone or vessel, after removing the KQ'MIIO}; from the first reaction zone, preferably at a rate comparable to its production. In prior chemical studies, K MnO had been produced by the following reaction carried out with powdered'materials in the dry state at about 800 C.

The compound had also been produced by a high temperature decomposition of K MnO as follows:

Both of these methods are technically impractical and result in an anhydrous product. l

The present invention is based upon the following reactions:

KOH-H O sol'n KGB-H1O soln 2K3M11O4+%O2+HgO )2KqMnO4l-2KOH -310 0. So far as known, this represents the first time a process has been based upon Equation 5, which is especially sigaxid 6in-separate zones. K M-nO is rapidly produced a nificant as employed in the production of K MnO The equation represents reaction in an aqueous melt at a relatively low temperature, which provides a practical commercial process producing arr aqueous product which; is readily further processed,=and.the operating conditions; V such as temperature, pressure and .concentration'arecom V mercially attractive. Reaction 6 represents avery useful andeconomic process' 'of manufacturing K MnO starting with K Mn'O ,3 advantageously the product oi Equation 5; 4

Each reaction may be carried out atja favorable rela tively low temperature, which is especially advantageous in materially reducing-corrosion. Also; the'solids and solutions-are handled and processed with less 'difliculty;

and construction, maintenance and'opera tion of the ves sels, filters, pumps-andother equipment are facilitated. 1 Reaction 6 may take; place in the same reaction zone Reaction; 5 furnishing an adequate. supply of oxygen 7 for that purpose and removing the K MnO whioh crys tallizes as it is produced; Reaction 6 may take place 2 while Reaction 5 occurs with the continued addition of themanganeseoxidm Alternativelm Reaction 5 maybe completed withoutsubstantial-,produotion of K MnO -according to Reactiono, and thereafter, the K MnO may be oxidized to lint I110; accordingto Reaction 6.

1 centration is preferably alien- 65% droxide melt at a temperature of about 170 C. to 310 C., preferably about 220C. to 260 C. The reaction'rate is greater at the higher temperatures, while corrosion is reduced at the lower temperatures. Further increase in temperature is preferably'avoidedi to avoid possible decomposition of K MnO to 90%, by weight.

' However, the concentration and reaction'temperature may be varied. t

It is also preferred that the melt contain an excess of p ota'ssiurn" hydroxide over the theoretical molar ratio to manganese dioxide of 4: 1. A considerable molar excess of potassium -hydroxide.is-preferably-. employed, on the order of 30m 60:1 or greater, which provides a melt of suitable viscosity. In this connection, it will be ap parent that Equation 5 will be appropriately varied when the manganese oxide is other than manganese dioxide, and

a the potassium hydroxide and potassium manganatere- It is preferred in theinvention to withdraw the K M11O produced-in Reaction 5- at a rate:comparable to or approximately the same as itslrate of production, and oxidize it in a separate second zoneaccording to reaction 6 In this manner, Reaction ,6 and the K MnO product are not:

' complicated by the presence" of significant quantities of manganese oxide,;the starting material in Reaction -5. When carryin-goutboth reactions in one zone at the same 'time',- unractedlrnanganese oxide is found in the K MnO crystalline product,-and such is not the cas e when the rotation; aree rr'ieaom in separate zones. 7

' Further advantages accrue from carrying out Reactions,

separately and in-h ighyield, and it may be used for other purposes, .r rerm pie, as an'oxidizing agent. Each reaction is individually controlled, sothat the manganese oxide is; converted to K2MHQ4- in highyield and in asuccessful' continuouseonimerci-al process. e 7 1 In certain of its broader aspects, the invention involves,

then, an improvement in the production of K Mi1Q .liyv

oxidizinga manganese oxide in an aqueous potassium hyf droxrde' melt. The improvement comprises adding man-- quireme'n'ts will 'badjustedjaccordingly.

l The reaction proceedswith vigorous agitation while pro' viding a potassium manganate having amanganese valence ofgreater than 5Qiri' themelt. A quantity of the ma'nganate isjadded initially; .andfurthermanganate is'added con-' process. It"i s" preferr'ed tomaintain-th'e'molar ratio of KMnO or'KMnO tomangariese dioxide at aboutflA'zl or greater, and further preferably, at 251 0r greater. Since K MnO is relatively insoluble,ait is preferable not to provide a great excess, such as will interfere with agita- 1 tion and mixing.

' The manganese oxide is added at a'rate not substantially greater than the rate of oxidation to K MnO or oxidation of the manganeseto' a val'ence of '5. The oxide may be"addedintermittently orv continuously, care being taken-that at no time is :a considerable quantity of unreacted Mn0 present. The rate at which'the manganese oxidesh'oiild be addediis'best determined: empirically, for

eacli s'etoficondit'ions. 'i The" examples which follow are. a

. illustrati eof. substantially maximum rates of addition.

ganes'e oxideto; the melt containing .a'potassiuml manga natelhavingamanganese'valence of greater than}, and

oxidizing the manganese oxid e'to K MnO by. reaction with the potassiumlmangan'ate. The preferred proces s also includes providing a rate of manganese oxide additio n'lwhich is' not substantially greater. than .its rate of oxidation to' K Mn0;. The KgMno is advantageously 'oxid-izedfto' Kay 1110;. preferablylin a separate reaction zone. The inventionthus provides commercially impo'r:

' tant advantages in" the production of K MnO and pro- 7 vides a practical;.processffor the production of K MnO The prlor problems are overcome, so that it is no longer necessary to carry out the much more cumbersome and expensive production of 'K MnQ, by roasting. Also, the

rate of production per unit volume is many times greater. The invention contemplates the oxidation'of an oxidic The-reaction mixture also :can be analyzed iromi time to time'for KgMnOg-contentand' for- MnO content, todeter mine the rate of oxidation, for adjusting the rate of. manganese oxide"addition.- I Q Y While Reaction 5 advantageously does'n'ot require an oxygen-containing gas;suchmay be'provi'ded inintimate manganese compound wherein the manganese has a" valence of less than 5. 1 Various manganeseloxides'having manganese oxides front permanganate reactions, e.g.,' 5MnO -K O-35H Q, electrolytically and chemically pro:

duced manganese oxides manganese oxide hydrates,- and manganese oxides or oxide hydrates-combined with alkali metals may be employeds s s I Reactionj' is carried out in an aqueous potassium. by

a manganese valence of-fr orn 2 to 4,;alone. or in com 'bination, pure orimpure, may be employed. For example, 'pyrolusite containing on.the. order: of 87% of MnO calcined rhodochrosite, which isapproximately M11 0;

I dispersion through-'the' 'mixture for concomitant reaction according-to the .followingrequationr I (7); 2Mno;+61 on+ /2'o e zromnogsmo 1 How ve' Reaction 5 is apparently more rapid, so that under th'e' -defiiied conditions including maintaining at least a steiehieiaetfie amount of potassium manganate having a man a'n e valence at, greater than 5, inthefmelt, the production" of Kill/ n0} according {to-Reaction 7 would important. 7 I V V The reactions caribe entertains batch; semi-continuousor 'coritinuusoperation: For: continuous typeoperaa tion, it'is era ure necessaryterepuee the" potassium hydroxi consumed inRaction' 5., and this may bedone at lea-st in par't by cycling the potassiumhydroxide pro ducedinthe'sec'ena zone EY-Ritiii 6 and otassium hydroxide added tothescofidlzon'e arid subsecluent-l-y withdrawn in more co centr ted form-where the reactions are carried out insep rste mes; "meanness are potassi hydroxide requiremenmay be addedintermittently-oicontinuously in the form or aqiieeus-potassium liydroxide The potassium hydroxide con- 7 p arent not b'e-"so great asito render thei'modific-atiori V solution, which advantageously contains about 50% KOH, by weight, or greater. An equilibrium is reached in the melt by removal of water by evaporation, so that the KOH concentration is readilygmaintained between 65% and 90%.

The K MnO is very' soluble and remains in solution. It may be further oxidized to K MnO in the same vessel, the latter being withdrawn from time to time ,as it;

crystallizes out of solution, When operating in'this mannor, an oxygen-containing gas must be supplied to the melt to furnish the requirements of the further oxidation. The conditions are comparable to those subsequently described for the further'oxidation. It ispreferred,

however, to intermittently-or continuously withdraw the K MnO about as fast ash is' produced, in its solution, and pass it to a second reaction zone. The reaction in the second zone may take place at about the same temperature.

In the second reaction zone, it is again preferred that the melt contain about 65% to 90% of potassium hydroxide, by Weight. The reaction maybe carried out above the solidification point of the mixture, and is pref erably carried out at about 140 C. to 310 C. It isfurther preferred that the melt be maintained at a temperature of about 210 C. to 230 C. The melt is vigorously agitated, and air or other oxygen-containing gas is' intimately-mixed therewith, to provideabout 4 or more times the theoretical amount of oxygen.

Air is the preferred oxygen-containing gas, for coo-- nomic reasons, but oxygen, air enriched with oxygen, or

a'mixture of oxygen and an-inert gas might be employed.

The oxygen-containing gas is preferably under substantially atmospheric pressure plus any differential required to overcome the resistance to gas flow, but subatmospheric or superatmospheric pressures can be provided with appropriateadjustment of the conditions of temperature and potassium hydroxide concentration. When air is employed, it is preferred to contact the melt with a quantity equivalent to 4 or more times the theoretically required quantity of oxygen.

The K MnO solution from the first reaction is intermittently or continuously introduced into the melt. It is preferred to maintain a high concentration of K MnO in the melt, on the order of about 200 to 400 grams per liter, for example. The K MnO is very soluble, and is therefore readily oxidized to K MnO in the homogeneous solution, more readily than in the case of a heterogeneous mixture, as is the case when the further oxidation is carried out concomitantly and in the same zone with Reaction 5.

The K MnO is relatively insoluble and precipitates out of the reaction mixture. It can be separated by conventional methods, such as settling and decantation, centrifugation, or filtration. The reaction can be carried out in batch, semi-continuous or continuous operation. It is preferably carried out in a continuous manner, supplying K MnO solution to the reaction zone and withdrawing K MnO crystals continuously or periodically as they are I produced. Aqueous potassium hydroxide solution of at least 50% KOH is added to the second zone to replace the KOH withdrawn with the K MnO Carrying out the process in successive steps in the foregoing manner, conversion to K MnO and to K MnO approaches the quantitative. The product of the first reaction may be, for example, an aqueous potassium hydroxide solution containing about 300-350 gramsv of K MnO per liter. The product of Reaction 6 initially contains adherent mother liquor, containing K MnO potassium hydroxide and water. After washing, the crystals contain about 80% to 90% of K MnO potassium hydroxide, Water, and minor impurities. The K MnO is removed by Washing and returned to the process,so that the yield of K MnO is practically quantita- Reactions 5 and 6 may be carried out in conventional apparatus, such as a vat or vats equipped with suitable means of agitation and means for dispersing air throughout the batch. Provision is made for introducing the reagents and for withdrawing the products. In the preferred process,' K MnO and K MnO are produced 'continuously or semi-continuously, in the manner illustrated schematically'in the attached drawing.

An aqueous potassium hydroxide melt is provided in a vessel 1, and initial quantities of manganese oxide and K MnO or KMnO are added to the melt. Agitation is provided, and the manganese oxide and potassium mangana te are added from time to time or continuously'. Makeup aqueous potassium hydroxide is also added,

according to its consumption. Bafiie means schematically illustrated by a baflie 2 is provided in the vessel 1, be-

tween the inlets and outlet for the materials entering and leaving the vessel. 7 a

'As" the production of K5MnO proceeds, the solution may'be allowed to overflow-through a conduit 3 into a second reaction vessel 4, thus favorably affecting the reaction equilibrium in vessel 1, and supplying the initial material for the oxidation in -the second vessel 4. An

aqueous potassium hydroxide melt is provided in the second vessel "4, and the vessel is supplied with means for introduction of air and heat, and for agitation. Aqueous potassium hydroxide solution of 50% concentration or greater issupplied-to the second vessel 4 from "time to v time, to replace material withdrawn, and it becomes conpreferably are used as makeup KOH solution supplied to the second vessel. 7

"Part of the K MnO slurry removed from the second vessel 4 is preferably cycled directly to the first vessel 1, through a conduit 7, without filtering This material serves for the reaction in the first vessel 1, supplying both the K MnO and KOH requirements. In continuous type operation, it preferably corresponds to about two-thirds of the K MnQ, withdrawn from the second vessel 4. Of the K MnO cycled to the first vessel, about one-half takes part in the reaction, and the remainder constitutes an excess and is continuously cycled between the first and second vessels.

The manganese oxide in the first vessel is substantially prevented from entering the second vessel 4 by the bafiie 2 and also owing to a relatively small flow rate. The rate of How is such that the average residence or retention time for each particle is greater than the reaction time for the manganese oxide. The average residence time may be, for example, from 1 to 3'hours, while the oxidation of the manganese'oxide may require about 15 to '20 minutes or less, as subsequently exemplified. Consequently, at most a very smail amount of the oxide reaches the second vessel 4. 'In the second vessel, the average residence time may be about 1 to 2 hours, during which the small quantity of manganese oxide may be oxidized. The result is that very little if any unreacted manganese oxide will appear in the K MnO product.

An advantage of the process is that the heat requirements may be supplied entirely to one vessel, the second vessel 4. With the relatively low temperatures involved, the thermal eificiency can be very high. The initial potassium hydroxide melt for both vessels may be prepared in the second vessel by evaporating water from 50% KOH solution.

As the reactions proceed, heat is supplied to the second vessel, concentrating the additional 50% potassium hydroxide solution subsequently added and furnishing the heat required to maintain the reaction temperature. The hot K MnO, slurry cycled from the second vessel 4 to the first vessel 1 supplies the heat necessary to mainoperation 7 7 continuous. type s operation', e ther "QIIQTQI. two -vats, to

1 simple and inexpensive-equipment; is substitutedg iopana t fentireseriesof roasters;;having the aforementioned dlsratio'nalr timegisgreatlkreducedaand.amuch-mgm 'fieient 1 processisgprovidedr The requirements infir ofihef gen conta-iningz, gas are less;carbonate is formed byabsorption of :carbon dioxide from the air; The auj-dispersion'is'muph more intimate,

of th melts 'stir verywell, so that the ower 7 require- 'ment is low as -is the-wear on the stirring apparatus tratives j duce-80%':'KOH having ab volume-of l lit ersi F'Ihsolin 'tio'n iS-maintainedat 22O Ci, and SOOTgranis of K lb/H; l V or .400 grarns -of 'KMnQ4 areadded iiiitiallyfl 100 grams: of pyrolusite' 37% M110 fare; mace and iallowed to arewadded' and allowed to react for 1-5fminutes, 'th'ree;. product'of the oxidation reaction is an aqueousfpotas 1 K MnO by weight.

7 provided with means for introducing air.

KQMnOQ. per liter per minute.

tain the'reaction temperature-in the latter vesseL-thefirst vessel 'then. operat' g at aslightly; lower temperature 7 iA-inumber; ofsadditional 'advantages flow from the new process; .whi'eliris new; Ieminently: suited for? commercial- The 1proeesscarr be; carried out .inbatch or- 5;

produce large quantitics of K MnQg-and-KiMno The advantages;' The produet'sfareobtained'ina state oi hi hwpurityr The-dust problenr of -roasti g ifi eliminated. Op 7 cons erablyrreslu slri and accompanying advantage correspondingly and the reactions are improvedcorrespgndinglyz- Each 7 The following? examples are furnished .toassistpro-l viding V a complete understanding- 0fthe invention;-.but it c o b d rst rr a a h r ve t ni not ite thereto nor to the quantities; .materia:1 s,; conditions pros d .il ns ra d er ;which: are: merely illus a fEiqinplal,

Aqueous 1 potassium hydinxide is --"evaiporated react for awn-rs; minutes,- hile agitating the' mixture',

, Then,- ZOOgrams-of K MnO and 100. grams ofpyrolusite containing 300 grams of K MnO perv liter are placed in a reaction vessel equipped with an efficient agitator and The solution" may be prepared according. to'Exarnplel or-according to the succeeding examples. The 'solution or melt is maintained 'at a temperature of 225 C.

' The mixture'is agitated vigorously, and-in excess of- 7 four times the theoretical quantity of oxygen in the -form 'of' air is intimately mixed therewith. Intima-te mixture sis obtained'by .violent agitation whileintroducing air over.

*the mixture; so as to intimatelydisperse fine bubbles of airin the suspension; 7 Alternatively air introduced through atubie direotly into the mixture. v p Oxidation proceedsqattherate of about 2 grams of The'K MnO consumed.

iscontinuOuSIy'replaced aswith the solution from Ex-160 ample 11L K MnO crystallizes out of the reaction. mix-' 'ture, is Withdrawn from time to time in the form of ,a

slurry in potassium hydroxides'olutiomand is separated from the mother liqu0r:by-filtra'tion.' Part of the slurry may be used in the methodof. Example 1, forthe produc- 7 tion ofladdit'ional K MnQ .Makeup potassium hydroxide solution of 50% strength or greater. is added to the vessel?" 1 'The filter cake er" K MnO is washed,with[60% aqueous potassium hydroxide solutionat 100 C., and

thelliqu-id. is removed from the calgeby suction. The V filtrate isfrecycledto the reaction .vessel whereinithe" K MnQ -is produced, and the washes are employed as f theEabove makeup solution;

. 100}. grams :-of.- caloin q 50 gallon'sof V maintained at. 220 C.- In themanner of Exampleg l 7601 immd 1 sinn r- 5090111168 or M Qe e.

served, and themanganese oxi'de isradded substantially- V tozr errrpvejthe. liquor 'contains 82%,to 90.%,;o K Mno anemone h d ox de. w e n l hl ifi -s- Thei-x ehi ba edmm KrM l s a i fli "l iaqm l r The? procedure.of.-Examp1e hislrep eated; except that an. 85 KOH melt" is atr'atemperature of.

abdnrslou'q c; .Therjeactioiir i s areiLredu ed from 5 15 @mefxgmno; product solution is.sulistantiallythesame' f; a I

jfExmpleyig r V 1 V pile:l is,repeated exceptlhat.

as-sedan ed. rhodochrosite 'are. employed. for;

each addition insteadnf. of pyrolusite. The

remaining' conditions are the same, .exceptthetflie .reacee ab -2 am e' s eek The product'is substantially the same. 1 1

j; 77 V p 7 aqueous potassium. hydroxide-are? added. ;10. PO1ID. of; pyrolusite a'reradded and. allowed: to reaot forsabodt l5iminutes. Thereafterpthree succes sive ,additiOns'of- ZQ poundsof K Mn0 and. .10. pounds. of pyrolusite --are made', .with;reaction intervalsof -15: ut'esf, The product and.yield aresubstantially'the: same:

' as inExample. 1. 7 r The invention thus provides a new process forpi'oducingQ K MnO, and for producing. KMnO which constitutes a substantialrimprovementoverthelprior. methods. and overcomes their disadvantages;w A manganese. oxide: isvery advantageously oxidizediby reaction with apotassiurn. manganate having a" manganese valence of greaterth-an 5.

A' major. characteristicv of the process is thatlthe inanganesenxide addedartarate whichis not, substantially greater than its; rate of oxidation .to- When this inipontant condition. is not. ob?

more rapidly than it isoxidized, the excessoxide'inthe suspension swells up, prevents adequate agitation and properm=ixing,-so.that it is very difficultto'carryv outithe l reaction. The addition of the manganese oxide aceord ing to theinventionalso takes advantage of thereaction rate andprovides. a successful continuous 'process. The manganese dioxide is substantially consumed; so tha tthes' K5M'n01,,. solution conveyed. to the second. reaction. zone for production. of K MnO contains an insubstantial' quantityof. manganese dioxide, avoiding contamination V of the K 'MnO product. The process of'th vention'is rapid and reliable ,".and. produces high qualityproducts in'high yields. .The, consumption Qof materials is a minimum, and the operation f is carried out but a' small equipment installation with:

low investment; powerg heat labor and maintenance l requirements The invention provides a. very advanta geous solutionto the problem of oxidizing a manganese V oxide inan aqueousmelt, rendering the. process suitable for largescale commercialToperation. V Theinvention is hereby claimed as iollows y 1 In a process for producing K MnO; by. oxidizing a manganese oxide'having a manganese yalence of less,

than 5 in a hotaqueouspotassiu'm" hydroxide solution;

the irriprovem'ent which comprises adding saidimanga nese oxide to sa-idjsolution containing a potassium manganate having a manganese valence ofv greater. than 5,, oxidizing said manganese oxide to K MnO by reaction" with said potassium manganate, the rate of said manganese oxide addition being not substantiallyzgreater' than its rate (if-oxidation to K MriOg and oxidizing-"the K n/ n0 produced toK MnQ a V 2.. Ina process: for. producing KQMnO by oxidizing: a manganese. oxide. having a manganese; valence oiless:

' 'j fhefprpdupt afiteriwashin f jidapplioation-of suction. 75. than .5 in a hot aqueous potassium hydroxide solutiong the improvement which comprises adding said manganese oxide to said solution containing a potassium manganate having a manganese valence of greater than 5, oxidizing said manganese oxide to K MnO by reaction with said potassium manganate, maintaining the average manganese valence in said solution at a value of at least 5, the rate of said manganese oxide'addition being not substantially greater than its rate of oxidation to K MnO and oxidizing the K Mn produced to KQMHOQ.

3. In a process for producing K MnO by oxidizing a manganese oxide having a manganese valence of less than in a hot aqueous potassium hydroxide solution, the improvement which comprises adding said manganese oxide to said solution containing a potassium manganate having a manganese valence of greater than 5, oxidizing said manganese oxide to K MnO by reaction with said potassium manganate, the rate of said manganese oxide addition being not substantially greater than its rate of oxidation to K MnO removing the K MnO produced, and oxidizing the K MnO removed to K MnO in a separate reaction zone.

4. In a process for producing K MnO by oxidizing a manganese oxide having a manganese valence of less than 5 in a hot aqueous potassium hydroxide solution, the improvement which comprises providing an aqueous about 65% to 90% potassium hydroxide solution and maintaining it at a temperature of about 220 C. to 260 0, adding said manganese oxide to said solution containing a potassium manganate having a manganese valence of greater than 5, oxidizing said manganese oxide to I 3MHO4 by reaction with said potassium manganate, the rate of said manganese oxide addition being not substantially greater than its rate of oxidation to K MnO removing the K MnO produced, and oxidizing the K MnO removed to K MnO in an aqueous about 65 to 90% potassium hydroxide solution maintained at a temperature of about 210 C. to 230 C. in a separate reaction zone.

5. In a process for producing K MnO by oxidizing manganese dioxide in a hot aqueous potassium hydroxide solution, the improvement which comprises adding said manganese oxide to said solution containing an excess of a potassium manganate having a manganese valence of greater than 5, oxidizing said manganese dioxide to K MnO by reaction with said potassium manganate, the rate of said manganese dioxide addition being not substantially greater than its rate of oxidation to K MnO removing the K MnOr, produced, and oxidizing the K Mn0 removed to K MnQ, in a separate reaction zone.

6. In a process for producing K MnO by oxidizing manganese dioxide in a hot aqueous potassium hydroxide solution, the improvement which comprises providing an aqueous about 65% to 90% potassium hydroxide solution and maintaining it at a temperature of about 220 C. to 260 C., adding said manganese dioxide to said solution containing a potassium manganate having a manganese valence of greater than 5, oxidizing said manganese dioxide to K MnQ; by reaction with said potassium manganate, maintaining the molar ratio of said potassium manganate to manganese dioxide in said solution at a value of at least about 1.4:1, the rate of said manganese dioxide addition being not substantially greater than its rate of oxidation to K MnO removing the K Mn0 produced, and oxidizing the K MnO removed to K MnO in an aqueous about 65% to 90% potassium hydroxide solution maintained at a temperature of about 210 C. to 230 C. in a separate reaction zone.

7. The process for producing K MnO which comprises adding a manganese oxide having a valence of less than 5 to a hot aqueous about 65% to 90% potassium hydroxide solution at a temperature of about 170 C. to 310 C., providing a potassium manganate having a manganese valence of greater than said solution, oxidizing said manganese oxide to K MnO by reaction with said potassium manganate, therate of said manganese oxide addition being not substantially greater than its rate of oxidation to K' MnO removing the K MnO produced, and oxidizing the K MnO removed to K MnO in a separate reaction zone by intimately mixing an oxygen-containing gas with an aqueous about 65% to potassium hydroxide solution of the former at a temperature of about C. to about 310 C.

8. The process which comprises adding a manganese oxide having a manganese valence of less than 5 to a hot aqueous potassium hydroxide solution containing a potassium manganate having a manganese valence of greater than 5, and oxidizing said manganese oxide to K MnO by reaction with said potassium manganate, the

rate of said manganese oxide addition being not substantially greater than its rate of oxidation to K MnO 9. The process which comprises adding a manganese oxide having a manganese valence of less than 5 to a hot aqueous potassium hydroxide solution containing a potassium manganate having a manganese valence of greater than 5, oxidizing said manganese oxide to K MnO by reaction with said potassium manganate, the rate of said manganese oxide addition being not substantially greater than its rate of oxidation to K MnO and removing the K MnO produced.

10. The process which comprises adding a manganese oxide having a manganese valence of less than 5 to a hot aqueous about 65% to 90% potassium hydroxide solution containing a potassium manganate having a manganese valence of greater than 5, maintaining said solution at a temperature of about C. to 310 C., and oxidizing said manganese oxide to K MnO by reaction with said potassium manganate, the rate of said manganese oxide addition being not substantially greated than its rate of oxidation to K MnO 11. The process which comprises adding manganese dioxide to a hot aqueous potassium hydroxide solution containing a potassium manganate having a manganese valence of greater than 5, maintaining an excess of said potassium manganate in said solution, and oxidizing said manganese dioxide to K MnO by reaction with said potassium manganate, the rate of said manganese dioxide addition being not substantially greater than its rate of oxidation to K MnO 12. The process which comprises adding manganese dioxide to a hot aqueous about 65% to 90% potassium hydroxide solution containing a potassium manganate having a manganese valence of greater than 5, maintaining said solution at a temperature of about 220 C. to 260 C, maintaining the molar ratio of said potassium manganate to manganese dioxide in said solution at a value of at least about 1.4: 1, and oxidizing said manganese dioxide to K MnO by reaction With said potassium manganate, the rate of said manganese dioxide addition being not substantially greater than its rate of oxidation to K3MHO4.

13. In a process for producing a potassium manganate by oxidizing a manganese oxide having a valence of less than 5 in a hot aqueous potassium hydroxide solution, the improvement which comprises continually maintaining in the solution a quantity of potassium manganate having a manganese valence of greater than 5 which is at least about stoichiometrically equivalent to the quantity of said manganese oxide in the solution.

14. In a process for producing a potassium manganate by oxidizing a manganese oxide having a valence of less than 5 in a hot aqueous potassium hydroxide solution, the improvement which comprises initially providing in the solution a quantity of potassium manganate having a manganese valence of greater than 5, adding said manga nese oxide to the solution, and continually maintaining in the solution a quantity of said potassium manganate 

1. IN A PROCESS FOR PRODUCING K2MNO4 BY OXIDIZING A MANGANESE OXIDE HAVING A MANGANESE VALENCE OF LESS THAN 5 IN A HOT AQUEOUS POTASSIUM HYDROXIDE SOLUTION, THE IMPROVEMENT WHICH COMPRISES ADDING SAID MANAGANESE OXIDE TO SAID SOLUTION CONTAINING A POTASSIUM MANGANATE HAVING A MANAGANESE VALENCE OF GREATER THAN 5, OXIDIZING SAID MANGANESE OXIDE TO K3MNO4 BY REACTION WITH SAID POTASSIUM MANGANATE, THE RATE OF SAID MANGANESE OXIDE ADDITION BEING NOT SUBSTANTIALLY GREATER THAN ITS RATE OF OXIDATION TO K3MNO4, AND OXIDIZING THE K3MNO4 PRODUCED TO K2MNO4. 